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Effect of deformation temperature on the hot compressive behavior of metal matrix composites wit

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RARE METALS VoL 26,No.2.Apr2oo7,p.182 E.mail:rill@ustb.edu.cn Available online at www.sciencedirect.com ScienceDirect Effect of deformation temperature oH the hot compressive behavior of metal matrix composites wiht misaligned whiskers LIAibin1),MENG Qingyuan ,GENGLinn,DENG Chunfeng andYANYiwu 1)School ofMaterials Science and Engineering,Harbin Institute ofTechnology,Harbin 150001,China 2)Department ofAstronautical Engineering and Mechanics,Harbin Institute ofTechnology,Harbin 150001,China (Received 2006-02-24) Abstract:Amulit—inclusion cellmodelisusedtoinvestigatethe effectofdeformationtemperature andwhisker rotation on htehot compressivebehaviorofmetalmatrix compositeswihtmisalignedwhiskers.Numerical results showthatdeforma- tiontemperatureinfluencesthework-hardeningbehavior ofthematrix andthe rotationbehavior ofthewhiskers.W讪in- creasing temperature,the work hardening rate of the matrix decreases,but the whisker rotation angle increases.Both whisker rotationandtheincrease ofdeformationtemperature caninduce reductionsintheload supportedbywhiskerand hteloadtransferredfrommatrixtowhisker.Additionally,itisfoundthatduringlarge straindeformation athighertempera- tares,the enhancing ofdeformationtemperature can rdeucethe effcet ofwhisker rotation.Meanwhile,the stress—strain eb. haviorofthe composietisrahter sensiitvetodeformationtemperature.At a relativelylowertemperature(150。C1.the com- opsiet exhibitsworkhardeningduetothematrixworkhardening,butat relaitvelyhighertemperatures(300。C and above), hte composite shows strain softening due to whisker rotation.It is also found that during hot compression at higher tern- peratures.the softening rateofthe compositedecreaseswithincreasingtemperature.111epredictde stress—strainbehaviorof htecompositeis approximatelyinagreementwiththe experimental results. Keywords:metalmatrixcomposiet;hotcompressivebehavior;deformationtemperature;finite elementmethod 【Thisstudywasfinancially supportedbytheNationalNaturalScienceFoundationofChina(No.50071008).】 1.Introduction requires an understanding of the effect of tempera- ture and reifnorcement rotation on the hot deforma. Metal matrix composites with discontinuous re. tion behavior of hte composites. inforcements have received a great deal of aRention In the recent years,a number of investigations because the addition of brittle reinforcements into 『4.141 have been ocnducted on hte nifluences ofde. hte ductilematrix caninducethe compositestohave formation temperature,strain rate,reinforcement superior properties,such as increased sffength and volume fraction,and reinforcement distribution on higher stifness at room temperature or elevated hte mechanical behavior of the discontinuously re— etmperatures compared with monofithic metallic inforced metal matrix composites during hot def0r_ materials[1-3】.In generla,the ocmposiets ale often mation,in which,deformation temperature is the subjected to the hot plastic forming,during which most important factor.It has been found from these hte reinforcements canbemisaligned awayfromthe experiments[10-14]that the strain-softening behav- 1oading direction and rotated toward a more stable ior appears during hot compression ofthe SiCw,A1 position.Therefore,optimization of the mechanical composites and the strain.softening phenomenon of behavior of hte composites during hot deformation the composites is related to the whisker behaviors Corresponding author:LI Aibin E-mail:aibinlee@hit.edu.cn 维普资讯 http://www.cqvip.com

UA.B.eta1.,Effectofdeformationtemperatureonthehot compressivebehaviorof... l83 including whisker rotation and breakage.Deforma— itontemperature affects significantlythe stress.strain behavior of the aluminum matrix composites witl1 has also been employed to investigate the deforma- iton behavior of the composites[18].To date,no systemic studies regardingthe effectsofdeformation temperature on the hot compressive behavior ofthe composites with misaligned whiskers have been conducted using he tinite felement method. In this study,the multi.inclusion cell model is employedto simulatetheprocessofwhiskerrotation ndtahe evolution of stress field ofthe composite at ceramic whiskers oriented rndomlay[12】and para1. 1eled to the 1oading dircteion『13].Meanwhile,de. formation temperature also influences the rotation nd abreakage of whiskers parallel and perpendicular to the 1oading direction during hot deformation of he SitCw,A1 composites r14].These studies based on the experiments have shown that deformation temperaturehas a signiicafnt effectonthe composite ehaviors duribng hot compression.However,few experimental and numerical researches have been diferent temperatures during large strain deforma- iton.Themulif.inclusion unit elc model is based on he unifortm and periodic arrangement ofthe whisk. ers misaligned from the compressive direction.In he motdel,many whiskers surrounded by metal ma- trix are again embedded in an equivalent composite materil ian order to simulate the actual experimental situation.During hot compressive deformation at carried out on the effect of deformation temperature onthehot compressivebehaviorofthemetalmatrix composite wih tmisaligned whiskers. Recently,the finite element method has been widely used to investigate the mechanical properties lower and higher temperatures,the effects of whisker rotation andmatrix workhardening arepre— nd raesidual stress of the composites r15.18].The influences of volme furaction,aspect ratio,shape nd spadala distribution of reinforcements on the de— ictded,and then the deformation behavior of the composites is further analyzed.The numerical re— sultsarecomparedwihtthe experimentalones. formation behavior ofthe composites have been in— vestigated by the axisyrnmetric model wih a sitngle ncliusion『15].The ere印behavior ofthe composites reinforced wih misatligned short fibers has been predicted by the plane strain model with a single fi— 2.Materials and experimental methods Hot compressive tests of the 20 vo1.% SiCw/6061A1 composites,which were prepared by squeeze casting followed by hot extrusion,were er br16].The three.dimensional fniite element mode1 based on a single fier habs been used to analyze the effect of reinforcement orientation on the tensile re— conducted for compaftsons with the results of the numerical analysis.The reinforcement used here is sponse ofthe composites at room temperature[17]. Moreove ̄the muli.itnclusion unit cell model wih a tnumber of the randomly distributed reinforcements 3-SiCwhiskerswihtthefollowingpropertiesthatare listed in T{lble 1. Table1.Propertiesof SiC n order Ito better investigate the whisker rotation ehavior bduring hot compression,the whisker often— attion angle etween tbhe whisker axis and the wih mtisaligned whiskers were performed in the air wih a sttrain rate of 0.083 s~.The compressive temperatures were selectd eto be 150。C(1ower hatn he trecrystallization temperature)300。C,400。C,and compressive direction was chosen to be 30。.The iametder and length ofthe cylindrical compressive 5o0。C(higherthanthe recrystallizationtemperature) Each ofthe specimens was compressed to a height of 8 mlrl with a reduction of4 mlrl in the axis direc- specimenare 8mlrland 12mlrl,respectively. Uniaxial hot compressive tests of he composites t维普资讯 http://www.cqvip.com

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LiA.B.et .Effect of deformation temperature on the hot compressive behavior of l8s culatedbythefollowing equation w= cr。== [:攀cr。 ,c ], 。== 一[: 。 ,c ] c is the total volume of the composite in t is the volume of 阵 州 l, m=去阵 f]c2 , where,Vwisthetotal volme oftuhewhiskers, is the volume of the,.h dementt of the whisk. ers, w,is the average stress in the compressive di— where, rection in the j-ht element of he whtiskers,o-mi is heaverage sttressinthe compressivedirectionofthe he itnternal embedded cell, the k-th element in the internal embedded f.山elementofthematrix, rm isthevolume Ofthe matrix, f isthevolmeoftuhei-thelementofthe matrix,Nw and Nm are the total numbers of cell,o-ck and ck are the average true stress-strain n tihe compressive direction in the k-th element of he tcomposite,respectively.Ⅳcisthetotalnumberof elementsinthe embeddedcel1. Tobetter analyzethemechanicalpropertiesofthe matrix and whisker,it is necessary to calculate the elements of he twhiskers nd amatrix,respectively. In the simulation,SiC whisker is taken to be lin. ear elasticandisotropic.6061A1.alloymatrix canbe approximated from the experimental results as bom linear elastic and plastic material wih ltinear iso. ropic work thardening. matrix stress o-m nd tahe whisker stress o-w in the embedded cel1.111e whisker average stress o-、vand matrix average stress o-m m the compressive direc。 For lrge starain elastoplstaic problems,the incre- mental constitutive equation in updated Lagrangin aifnite elementformulationcanbewritenas itonarecalculatedbythefollowing equation: = DOJI t eld=(1/9)(酬G)(3G+矗) 『2G(6 6Ⅳ+ : 6 6“)一 :f is the Poisson ratio, is the tekl (3) where, is the increment of Jaumann stress elements with second-order Gaussin iantegration points.111e adequacy of finite element discretization is checked by repeating a calculation using refined meshes until a satisfactory computational accuracy is obtained. tenser,f P“is the increment of the strain tensor, t D is the tangentil constaitutive tensor,G is the shear modulus, Euler deviator stress components. Thefinite elementmethodisusedto calculatethe stress.strain field quantiites in the whiskers and ma- trix during compression utilizing an updated La-- hemateriaTl surroundingthemulti.inclusion unit cell is taken to be a homogeneous composite mate. rial equivalent to the embedded cell composite in mechanical properties.111e property parameters of heetquivalentmaterial canbe obtainedbymeans of grange formulation.Tllis numerical scheme uses the principle of virtual work to calculate incremental displacements,which through appropriate constitu- itve relations yield elemental stresses.In this formu. he itterative computation.Before computation,the matrix property parameters are considered to be the properties of he equivatlent composite materia1. - 1ation,the nonlinear response of the matedal is ap- proximated through an incremental approach which ter iteration,the properties of the embedded cell composite obtainedfrom eachiterative computation re ianput into the equivalent composite material for entails applying incremental displacements to the body until the applied extemal loading is balanced bythe sum oftheintemalnodalforces.nlenumeri- cal models were constructed using two-dimensional 4..node quadrilateral elements and 6..node triangulr ahe subsequent itteration until the error of results compared with previous iteration is suficientlfy smal1. 维普资讯 http://www.cqvip.com

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UA.最 a1..Effect of deformation temperature on the hot compressive behavior of... l89 decrease in the whisker stress with increasing aD. whisker stress with increasing applied strain at plied strain(Fig.7).At 300。C,the flow stress and work.h ̄emg rate of the matrix decrease mark- 5oo。C is smaller relative to that at 300。C.n is knownthatthewhiskers can support sufficient stress when the whisker aspect ratio is larger than the edly(Fig.4),leading to the relatively smaller in- creaseinthewhisker stress仃ansferredfromthema. trix to the whiskers.On the other hand,the rotation whisker criticla aspect raito ac=a ̄o/as( fbis fracture strengthofthewhiskerand O's istheyield nglaeofthewhiskersincreases signiifcantly(Fig.6), makingthe decreaseinthewhisker stressinducedby strength of the matrix).which increases with in. creasing temperature.During hot compression at whisker rotation enhance markedly.Hence,the whisker stress decreases relatively quickly under compressive load at ihgher temperatures(Fig. 71. Fig.6.Predicted variations of the whisker current orientation angle with the overall strain岛at dif- ferent temperatures. 皇 \ sc iFg.7.Predicted variations of the whisker average stress o-finthe compressivedirectionwitlltheoverall strain晶at diferent temperatures. Fig.7 also indicates that the reduction rate ofthe higher temperatures,the whisker aspect ratio is much smaller than the whisker critical aspect ratio, nidicating that the whiskers play a smaller role in strengthening the composite at higher temperatures. Therefore,thedecreaseofthewhisker stressinduced by whisker rotation will be mark ̄y reduced at 5oo。C.On the other hand.enhancing the tempera- ture decreases the matrix flow stress and work-hardening rate(Fig.4)resulitng ni a decrease ni both the load supported bY the whiskers and the load仃ansferfromthematrixtothewhiskers.Hence. hte decrease in the whisker stress induced by whisker rotation will be further reduced at 500。C. Meanwhile,the smallerincreaseinthewhisker rota- tion angle(Fig.6)can only decrease the whisker stress slightly.In summary,the increase in tempera- ture can decrease the reduction rate of the whisker stress induced by whisker ortation. 4.3.Effect of deformation temperature on the load transferfrom the matrix to the whiskers 111e di rencebetween fw nad ,( w一 m),is defined as the stress transferred from the matrix to hte whiskers.Fig.8 shows the variation ofthe stress rtansferred from the matrix to the whiskers ( w一 m)with the overall srtain乓.It can be seen that the stress trnasf ̄:red from the matrix to the whisker decreases wiht increasing temperature. Meanwhile,aDparent peaks are observed in the curves obtained at both lower and higher tempera- tures.During hot deformation,the matrix work hardening induces an increase in the matrix flow srtess m(Fig.4),and whisker rotation causes a erduction in hte whisker-supported stress (Fig. 7).1eadingtoa significant reductionin stresstransfer fromthematrixtothewhiskersunder1argeloading. Hence,whisker rotation can reduce load transfer.It 维普资讯 http://www.cqvip.com

190 is alSOfoundthatthe reduction rateinthetransferred stress decreaseswithincreasingtemperaturebecause hte reduction in the whisker stress induced by whisker rotation decreases at higher temperature as showninFig.7. 曼 Fig.8.Predicted variation of the transfer stress o-mf witlI the overall strain£c at diferent tempera- tures. It is concluded tllat deformation temperature and whisker rotation reduce the load supported by the whiskers and hte load transferred from the matrix to hte whiskers.Meanwhile.during large strain defor- marion at higher temperatures,the increase in tem. perature resultsinthe decreasesinthe reduction rate of whisker-supported stress and transferred stress. T}liS suggests tllat the effect of whisker rotation be- comes weaker wiht increasing deformation tem- perature.Several studies on the whisker rotation be havior have been reported[12—14].Previous ex— perimental results have indicated tllat whisker rota- tion influences significantly the hot compressive deformation ofthe composites,and whisker rotation induces the reductions in the load supported by the whiskersandtheloadtransferredfromthematrixto hte whiskers.The present numerical results are con sistent witll the previous experimental results. 4.4.Effect of deformation temperature on the overall stress-strain behavior of the composites Accordingtothe above—statedmatrixandwhisker behaviors,the stress—strain behavior of the compos— ites Can be analyzed.Fig.9 illustrates the calculated RAREMETALS,Vo1.26,No.2.Apr2007 average stress—strain c一 c curves in the corn‘ pressive direction of the composites in the embed— ded cel1.It is apparent that the ocmposite stress c ni the compressive direction decreases with increas. ing temperature.Additionally,the composites are observed to show work hardening at the lower tem- perature of 150。C and strain softening at the higher temperatures between 300。C and 500。C.The pre— idcted trends of stress.strain behaviors of the corn- posites are in qualitative agreement with hte experi- mental resulst rFig.1 0). 高 \ & iFg.9.Predicted average stress-strain curves in the compressivedirection ofthe compositesinthe embed- dedcellatdiferenttemperatures. 高 \ Fig.10.Measured average stress-strain curves in hte compressivedirectionofthe compositesinthe embed- ded cell at diferent temperatures. At the lower temperature,the relatively smaller rotation of hte whiskers(Fig.6)induces the corre- 维普资讯 http://www.cqvip.com

IdA.B.et a1.,Effect of deformation temperature on the hot compressive behavior of… 191 sponding smaller reductions in the whisker carrying load ability(Fig.7),but the matrix work hardening is significant and the matirx flow stress is higher g.4),inducing the apparent work hardening of hte composites g.9).At ihgher etmperatures,the matrix exhibits hte relatively smaller work-hardening rate and flow stress of the matrix (Fig.4),while,the relatively lrager rotation of hte whiskers induces the corresponding 1rager reduc— itonsinthewhisker-carryingloadabiliyt(Fig.7)and hte load仃ansferred from the matrix to the whiskers (F .8),causing the apparent strain softening be— havior in the composites(Fig.9 .TI1is indicates that hte matrix work hardening induces work hardening of the composites at a lower temperature and whisker rotation causes strain softening ofthe com— posites at a higher temperature. Moreover,it is found that during large strain de— forrnarion at higher temperatures,the reduction rate ofthe composite stress becomes lower with increas— ing temperature.On the one hand,whisker rotation causes strain softening of the composites.On the otherhand,theincreaseintemperaturedecreasesthe reduction rate ni hte whisker-supported srtess(Fig.7) nad hte rtnasferred srtess(Fig.81.which is induced by whisker rotation,causing the effect of whisker rotation to become weaker wiht increasing deforma- tion temperature.Therefore,the effect of the strain softening of the composites is reduced with increas— ing deformation temperature(Fig.9、.The similra phenomenon has also been observed during the hot compressive deformation of the composites rein— forced by whiskers orientated randomly and paralle1 to hte loading direction『131. 5. Conclusions In this study,the mulit—inclusion unit cell model wiht a number of uniformly and perilously mis— laigned whiskers is successfully used t0 simulate the effects ofdeformationtemperatureandwhisker rota- iton on the hot compressive behavior of hte compos— itesduring1rage straindeformarion. Deformation temperature influences the me— chanical behavior of hte matrix significantly during hot compressive deformation.As the temperature increases,the flow stress and work hardening ofthe matrix decreases.TIlis results in a reduction in the resistance of the matirx to whisker rotation and an miprovement in the plastic flow of the matrix.It is found that the matrix work hardening at lower tem— peraturesis verymore signiifcantthanthat athigher temperatures because the dislocation density reduc— iton due to dynamic recovery at lower temperatures is much smaller than that due to dynamic recrystal— lization at ihgher temperatures. Deformation temperature and whisker rotation affectthemechanicalproperties ofthewhiskers sig— nificanfly during hot compressive deformation.1]he increases in deformation temperature and whisker ortation lead to the reductions in both the load sup— ported by the whiskers and the stress transfer from hte matrix to the whiskers.Meanwhile,it is found htat athighertemperatures,theincreasein deforma- iton temoerature decreases the reduction rates of both the load supported by the whiskers and the stress transfer from the matrix to the whiskers. hTerefore,enhancingthetemperaturecan reducethe effect of whisker rotation during 1arge strain defor- marion at higher temperatures.The reduction in the whisker stress induced by whisker rotation at hither temperature is more singiifcant than that at lower temperatures. The stress—strain behavior of the composite is rather sensitive to deformation temperature.At lower temperatures,the composite exhibits work harden— ing due to the matrix work hardening.but at rela- tively higher temperatures,the composite shows strain softening due to whisker rotation.It is also found that during hot compression at higher tern— peratures,the softening effect of the composiet be— comesweakerwithincreasingtemperature.Thepre— dicted stress..strain behavior ofthe composite is ap.. proximately in agreement wiht the experimental re— sults. 【1]Quigley B.E,Abbaschian GJ.,Wunderlin R.,and Mehrabian R.,Method for fabrication of alumi— num-alumina composites,Metal1.Trans.,1982,13A: 93. 维普资讯 http://www.cqvip.com

I92 RAREMETALS,Vo1.26,No.2,Apt2007 [2]Arsenault R…J Strengthening of aluminum aJloy 6061 byfiber andplatelet silicon carbide.MaWr ScL Eng.,1984,64:171. itculate-reinforced 6061+20%A1203 composie,t Mawr ScLEng.,2002,324A:157. [11】Spigarelli S.,CerriE.,CavaliereP.,andEvangeilsta E..Ananalysis ofhotformability ofthe6O61+20% [3】Nardone VC.and Strife J…R Analysis of the creep behavior of silicon carbide whisker reinforced 2121 A1203 composiebymeatnsofdifferent stabilitycrite- ria,Mawr Sci. ,2002,327A:144. A1(1l4),Metal1. ns.,1987,18A:109. [4]Lay B.and Boivin M.,Thermo-elasto-plasitc ehav—b iour of a metal matrix composite Al一6O61/SiC and he eftfect of a precipitate-free zone around the rein- [12]GengL.,Ochial S.,andHu J.Q,Compressiontest- iIl2 of a SiCw/A1 composite at temperature close to and above he soltidus ofthe matrix alloy,Mater.Sci. forcement, Mater Process.Techno1.,1995,55: 261. [5]Hong S.H.and Chung K.H.,Effect of vacuum hot pressing parameters onthetensile pmpe ̄es and mi- crosl ̄uctures of SiC-2124A1 composites,Mater ScL 三 ,1995,A194:165. 【6]HongS.H.andChungK.H., 1eeffectofprocessing parameters on mechanical properties of SiCw/2124A1 composiets, Mater Process.Techno1.. 1995.48:349. [7】Yoo YC.,Jeon J.S.,and Lee H.I.,The effect of SiC whiskers on the hot deformation behavior of SiCw/AA2124 composiets,Compos.Sci.Techno1., 1997.57:651. [8】Standford—ebale C.A.and Clyne T Exlrusion nad mgh—temperature deformation of fiebr-reinforced aluminumcomposite,ComposSciTechnoL,1989,36 (2):121. [9】Zhang W:L_,Zhang M.,and Gu M.Y,Wang D.Z., nad Yao Z.K Effcet of cold-rolling on tensile strength ofSiCw/A1 composiet,RareMet.,2003,22: 285. [10】CerriE.,Spigarelil S.,EvangelistaE.,andCavailere P.,Hot deformation and processnig maps of a par- En ,1998,A246:302. [13】Xiong Z.,Geng L.,and Yao C.K.,Invesitgation of gh-temperature deformation behavior of a SiC whisker reinforced 606l aluminum composiet, Compos.ScL Techno1.,199l0,39(2】:l17. [14]Zhang w L.,High Strain Deformation of SiC Whiskers ReinforcedAlumin Matrix Composites Dissertation],HarbinInsittuteofTechnology,Harbin, 2000:68. 【15】DuttaI.,Sims J.D.,andSeigenthalerD.M.,etaL,An naalytical study of residual stress effects on uniaxial deformation of whisker reinforced metal matirx composiet,Acta MetalL朋 ,1993,41:885. [16】Sorensen N…J A planar model smdy of creep in metalmatrixcompositeswithmisaligned shortfibers, ActaMetal1.Mawr.1993,41:2973. [17】Sorensen N J Suresh S.,Tvergaard V,and Nee- dleman A..E &ts ofminfomement orientation on htetensile responseofmetal-matrix,Compos.。^ Sci. 1995,A197:1. [18】Ghosh S.,NowakZ.,andLeeK.Tessellation.based computational methods for the characterization and naalysis of heterogeneous microsffuctures,Compo ̄ ScL TechnoL,1997.57:1187. 

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